In recent years, photo-fabrication processes for forming three-dimensional objects consisting of integrally laminated cured resin layers prepared by repeating a step of forming a cured resin layer by selectively irradiating a liquid photo-curable material with light have been proposed (see Japanese Patent Application Laid-open No. 247515/1985, USP No. 4,575,330 (Japanese Patent Application Laid-open No. 35966/1987), Japanese Patent Application Laid-open No. 101408/1987, Japanese Patent Application Laid-open No. 24119/1993).
A typical example of such a photo-fabrication process comprises forming a curable resin layer having a specified pattern by selectively irradiating with light using, for example, an ultraviolet radiation laser on the surface of a liquid photo-curable material or photo-curable resin composition, feeding the photo-curable resin composition equivalent to one layer to form another thin layer of the composition over this cured resin layer, and selectively irradiating this thin layer with light to form a new cured resin layer which is integrally laminated over the previously formed cured resin layer. This step is repeated a number of times, with or without changing the pattern in which the light is irradiated to form a three-dimensional object consisting of integrally laminated multiple cured resin layers. This photo-fabrication process has been attracting considerable attention, because the target three-dimensional object can easily be prepared in a short period of time even if it has a complicated shape.
The following resin compositions are photo-curable resin compositions useful in photo-fabrication processes:
(A) resin compositions containing a radically polymerizable compound such as urethane(meth)acrylate, oligoester(meth)acrylate, epoxy(meth)acrylate, thiol-ene compounds, photosensitive polyimide, and the like (see Japanese Patent Applications Laid-open No. 204915/1989, No. 208305/1990, and No. 160013/1991); PA1 (B) resin compositions containing a cationically polymerizable organic compound such as an epoxy compound, cyclic ether compound, cyclic lactone compound, cyclic acetal compound, cyclic thioether compound, spiro-orthoester compound, vinylether compound, and the like (see Japanese Patent Application Laid-open No. 213304/1989); PA1 (C) resin compositions containing a radically polymerizable organic compound and a cationic polymerizable organic compound (see Japanese Patent Applications Laid-open No. 28261/1990, No. 75618/1990, and No. 228413/1994). PA1 (A) a compound represented by the formula (1), ##STR2## wherein R.sup.1 and R.sup.2 independently represent a hydrogen atom or a methyl group; PA1 (B) a compound having a cyclohexene oxide structure; PA1 (C) a cationic photo-initiator; PA1 (D) an ethylenically unsaturated monomer; PA1 (E) a radical photo-initiator; and PA1 (F) a polyol having three or more hydroxyl groups.
These photo-curable resin compositions require low viscosity in order to form a smooth liquid level, as well as the ability to be rapidly cured upon irradiation. Additionally, minimal swelling of the cured products, and minimal deformation resulting from shrinkage during curing with light, or production defects, such as: production of warped parts, indented parts resulting in sink marks, or stretched parts resulting in overhanging parts, are also required.
Three-dimensional objects prepared by photo-fabrication methods have conventionally been used for design models and trial mechanical parts. High dimensional accordance with the design model in fine processing, mechanical strength, heat resistance, moisture resistance, and water resistance sufficient to withstand conditions of use are especially demanded of these trial mechanical parts.
However, no conventional resin composition can satisfy the above demands. The three-dimensional objects obtained by the photo-fabrication processes exhibit problems of deformation with the passage of time, resulting in of warped parts, or indented parts, or stretched parts (overhanging parts), because of residual strain due to the shrinkage during curing. These problems of deformation with the passage of time can be partly solved by the correction of the input data to the CAD. However, the correction is insufficient to account for modern requirements of intricate fineness and complication in shape, and to circumstantial variations of use.
Mechanical characteristics of three-dimensional objects prepared by photo-fabrication using conventional resin compositions containing an epoxy compound are degraded in the course of time in accordance with environmental conditions such as temperature and humidity. Therefore, use of conventional three-dimensional objects is unsuitable for an application requiring mechanical strength over an extended period of time.
Also, no three-dimensional object prepared using the conventional resin compositions is capable of meeting the requirements for the trial mechanical parts such as mechanical strength, dimensional accuracy, heat resistance, moisture resistance, water resistance, and the like.
The present invention has been developed in view of this situation and has an object of providing a novel photo-curable resin composition.
Another object of the present invention is to provide a photo-curable resin composition capable of being fabricated to produce three-dimensional objects which have mechanical strength and high dimensional accuracy and are suitable for trial mechanical parts.
Still another object of the present invention is to provide a photo-curable resin composition which can be fabricated to produce three-dimensional objects provided with lasting minimal deformation characteristics.
A further object of the present invention is to provide a photo-curable resin composition capable of being fabricated to produce a three-dimensional object provided with lasting minimal degradation in mechanical characteristics.
A still further object of the present invention is to provide a photo-curable resin composition capable of being fabricated to produce a three-dimensional object which can be used in water and high moisture environments.